A quiet phase: NIST optical tools produce ultra-low-noise microwave signals

Jun 27, 2011
Matt Kirchner, a University of Colorado graduate student, fine-tunes an ultra-stable microwave generator that he helps operate at NIST. Credit: Burrus/NIST

By combining advanced laser technologies in a new way, physicists at the National Institute of Standards and Technology (NIST) have generated microwave signals that are more pure and stable than those from conventional electronic sources. The apparatus could improve signal stability and resolution in radar, communications and navigation systems, and certain types of atomic clocks.

Described in , NIST's low-noise apparatus is a new application of combs, tools based on ultrafast lasers for precisely measuring , or colors, of light. Frequency combs are best known as the "gears" for experimental next-generation atomic clocks, where they convert to lower microwave frequencies, which can be counted electronically.

The new low-noise system is so good that NIST scientists actually had to make two copies of the apparatus just to have a separate tool precise enough to measure the system's performance. Each system is based on a continuous-wave laser with its frequency locked to the extremely stable length of an with a high "quality factor," assuring a steady and persistent signal. This laser, which emitted yellow light in the demonstration but could be another color, is connected to a frequency comb that transfers the high level of stability to microwaves. The transfer process greatly reduces—to one-thousandth of the previous level—random fluctuations in the peaks and valleys, or phase, of the electromagnetic waves over time scales of a second or less. This results in a stronger, purer signal at the exact desired frequency.

The base microwave signal is 1 gigahertz (GHz, or 1 billion cycles per second), which is the repetition rate of the ultrafast laser pulses that generate the frequency comb. The signal can also be a harmonic, or multiple, of that frequency. The laser illuminates a photodiode that produces a signal at 1 GHz or any multiple up to about 15 GHz. For example, many common radar systems use signals near 10 GHz.

NIST's low-noise oscillator might be useful in radar systems for detecting faint or slow-moving objects. The system might also be used to make operating at , such as the current international standard cesium atom clocks, , more stable. Other applications could include high-resolution analog-to-digital conversion of very fast signals, such as for communications or navigation, and radio astronomy that couples signals from space with arrival times at multiple antennas.

Explore further: Precision gas sensor could fit on a chip

More information: T.M. Fortier, M.S. Kirchner, F. Quinlan, J. Taylor, J.C. Bergquist, T. Rosenband, N. Lemke, A. Ludlow, Y. Jiang, C.W. Oates and S.A. Diddams. Generation of ultrastable microwaves via optical frequency division. Nature Photonics. Published online June 26, 2011.

Related Stories

Atomic fountain clocks are becoming still more stable

Mar 18, 2009

They are at present the most accurate clocks in the world: Caesium fountain clocks furnish the second accurate to 15 places after the decimal point. Until they reach this accuracy, caesium fountain clocks, however, need a ...

Atomic clock signals may be best shared by fiber-optics

Mar 02, 2007

Time and frequency information can be transferred between laboratories or to other users in several ways, often using the Global Positioning System (GPS). But today's best atomic clocks are so accurate—neither gaining nor ...

Enhanced LIDAR improves range, vibration measures

Feb 02, 2006

Scientists at the National Institute of Standards and Technology have demonstrated the use of an ultrafast laser "frequency comb" system for improved remote measurements of distance and vibration. The technology, ...

Optical Atomic Clock: A long look at the captured atoms

Feb 05, 2008

Optical clocks might become the atomic clocks of the future. Their "pendulum", i.e. the regular oscillation process which each clock needs, is an oscillation in the range of the visible light. As its frequency is higher than ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

Precision gas sensor could fit on a chip

Feb 27, 2015

Using their expertise in silicon optics, Cornell engineers have miniaturized a light source in the elusive mid-infrared (mid-IR) spectrum, effectively squeezing the capabilities of a large, tabletop laser onto a 1-millimeter ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

New research signals big future for quantum radar

Feb 26, 2015

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.